CISA KEV · catalog date Nov 3, 2021 · first observed Sep 1, 2026
Evidence dossier
CVE-2021-26858
Microsoft Exchange Server Remote Code Execution Vulnerability
Exploited in the wild (CISA KEV since Nov 3, 2021). microsoft reports CVSS 3.1 7.8. EPSS estimates 93.7% exploit likelihood as of Oct 21, 2026.
As of Oct 22, 2026
Normalized restatement
Microsoft Exchange Server Remote Code Execution Vulnerability
- State
- PUBLISHED
- Published
- Mar 2, 2021
- Updated
- Oct 1, 2026
- Evidence coverage
- 85%
Evidence chronology
What was known when
- Source dateFirst observed by CASCACISA KEVOriginal evidence ↗
Exploitation cataloged: Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
observed_exploitation- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
- Source dateSource date omittedFirst observed by CASCACISA-ADPOriginal evidence ↗
Record text: CISA ADP Vulnrichment
Inspect raw assertion
- Field
container- Value
- CISA ADP Vulnrichment
- Source dateSource date omittedFirst observed by CASCACVE ProgramOriginal evidence ↗
Record text: CVE Program Container
Inspect raw assertion
- Field
container- Value
- CVE Program Container
- Source dateSource date omittedFirst observed by CASCAmicrosoftOriginal evidence ↗
Record text: Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
container- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
- Source dateFirst observed by CASCAFIRST EPSSOriginal evidence ↗
EPSS score: 93.65% probability · 99.85th percentile
Inspect raw assertion
- Field
model_probability- Value
- Probability 0.936510000000; percentile 0.998450000000
FIRST EPSS · score date Oct 21, 2026 · 99.8th percentile · first observed Oct 21, 2026
microsoft · CVSS 3.1 · first observed Oct 1, 2026 · same-version scores align in this snapshot
Evidence detail
Source limits and decisions
Why each evidence state has this value
casca-unknown-reasons-v1The last verified source boundary remains in force for this claim.
- Revision
- evidence-policy-v1.1.0
- Cutoff
- Oct 22, 2026
- Resolution
- Review source contract
Eligible evidence is present for this bounded claim.
- Revision
- evidence-policy-v1.1.0
- Cutoff
- Oct 22, 2026
- Resolution
- None
Eligible evidence is present for this bounded claim.
- Revision
- casca-direct-cvss-eligibility-v1
- Cutoff
- Oct 22, 2026
- Resolution
- None
The cited source assertion is retained while canonical product linkage remains open.
- Revision
- casca-factor-d-obligations-v1
- Cutoff
- Oct 22, 2026
- Resolution
- Resolve identity
Source comparison
Who said what
Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
observed_exploitation- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
CISA ADP Vulnrichment
Inspect raw assertion
- Field
container- Value
- CISA ADP Vulnrichment
CVE Program Container
Inspect raw assertion
- Field
container- Value
- CVE Program Container
Microsoft Exchange Server Remote Code Execution Vulnerability
Inspect raw assertion
- Field
container- Value
- Microsoft Exchange Server Remote Code Execution Vulnerability
93.65% probability · 99.85th percentile
Inspect raw assertion
- Field
model_probability- Value
- Probability 0.936510000000; percentile 0.998450000000
Applicability
Cited product scope
Grouped from 1 configuration nodes in this exact snapshot. Visual grouping is navigational; asset exposure and root cause require cited evidence.
Identity source boundaries
- Cpe dictionary1,775,266 records · observed through 2026-07-21T06:45:29.809Z
27d65b0f-b718-4b4f-bb79-c47c68d09dfa - Cpe match643,502 records · observed through 2026-07-21T08:13:17.697Z
955dae73-7302-438b-aee1-058d7cc5d48e
25 scope groups
Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.00.0", "lessThan": "15.00.1395.012", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.00.0", "lessThan": "15.00.1473.006", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.00.0", "lessThan": "15.00.1497.012", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1531.012", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1591.018", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1713.010", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1779.008", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1847.012", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1913.012", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1979.008", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.2044.013", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.2106.013", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.2176.009", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1415.010", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.01.0", "lessThan": "15.01.1466.016", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0221.018", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.01.1979.006", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0397.011", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0464.015", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0659.012", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0595.008", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0529.013", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0721.013", "versionType": "custom"}]Canonical linkage remains open; the cited source assertion is retained below.
Inspect raw assertion
[{"status": "affected", "version": "15.02.0", "lessThan": "15.02.0792.010", "versionType": "custom"}]product-d87daca995d075bf30565cc429e7242a47683272975068df1d327ec1d8ff609cLinked exactInspect raw assertions
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 7
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
4df5bdb5-205d-4b64-a49a-0152afcf4a13
cpe:2.3:a:microsoft:exchange_server:2013:sp1:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 3
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
0c21f84b-e99c-451d-9eaf-6352fd2b0eaf
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 13
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
28fca0e8-7d27-4746-9731-91b834ca3e64
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 9
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
ca2ce223-aa49-49e6-ac32-59270eff55ad
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 17
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
051de6c4-7456-4c42-bc51-253208aadb4e
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 15
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
69af19dc-3d65-49a8-a85f-511085cdf27b
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 8
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
55284cf7-0d04-4216-83fe-4b1f9ca94207
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 5
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
9be04790-85a2-4078-88ce-1787bc5172e7
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 6
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
ccf101be-27fd-4e2d-a694-c606bd3d1ed7
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 2
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
da166f2a-d83b-4d50-ad0b-668d813e0585
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 23
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
36ce5c6d-9a04-41f5-ae7c-265779833649
cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 1
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
751fd35f-2ecd-4b75-9589-988cc6ad3058
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 20
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
73b3b3fe-7e85-4b86-a983-2c410ffef4b8
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 4
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
63e362cb-cf75-4b7e-a4b1-d6d84afcbb68
cpe:2.3:a:microsoft:exchange_server:2019:-:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 16
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
40d8a6db-9225-4a3f-ad76-192f6cccf002
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 14
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
075e907f-af2f-4c31-86c7-51972be412a1
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 18
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
ee320413-d2c9-4b28-89bf-361b44a3f0ff
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 22
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
d4ab3c25-cea8-4d66-aee4-953c8b17911a
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 24
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
44ecf39a-1de1-4870-a494-06a53494338d
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 10
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
4830d6a9-af74-480c-8f69-8648cd619980
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 11
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
079e1e3f-ff25-4b0d-ac98-191d6455a014
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 21
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
8a9fb275-7f17-48b2-b528-be89309d2af5
cpe:2.3:a:microsoft:exchange_server:2010:sp3:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 0
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
3e5ea9ad-1e84-4ab5-a1ef-3b9f2ac84755
cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 12
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
29805ec7-6403-44b9-91ec-109c087e98eb
cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:*- Official link
- Linked exact
- Role
- Vulnerable target
- Configuration
- 0 · node/0 · match 19
- Logic
- OR
- Version bounds
- No explicit bounds
- Match ID
104f96dc-e280-4e0a-8586-b043b55888c2
Affected-product evidence
Accepted scope and product mapping
0 canonical links · 2 source-reported links
Canonical linkage remains open; the cited source assertion is retained below.
Vendor specified only by source · Product specified only by source
- Source class
- Direct cve affected
- Assertions
- 24
- Mapping revision
- cpe23-exact-mapping-v1
- Observed cutoff
- Oct 22, 2026
Retained assertion IDs
06c00530-11cb-42e8-815c-d9896d558890182f36a4-a1ee-4582-9390-ac61f50bc6011ff0e714-9b1f-4086-bac5-b2df504a8d4a20413235-ca32-49f8-ba3c-9897e3841d5d26ab943c-a498-4385-97db-99273e7130fb2cffd77c-65f8-4887-b2d2-efe0f41bbf342de76874-e46e-4b27-9966-4c0b7299c63f3b4826d3-2bb9-4136-8f73-66ba40cd747f507c32dd-ca3d-45ad-ad7a-612ad03d2f09610317e1-7d85-43b9-a956-969c523f1e9f6ba3e6bf-0af7-44d6-946b-6f6823fbddb18618b359-68f9-47ad-82ac-ae28e1e55e6a88efea5a-1ace-4ce1-a0d0-29cab1915e6389e9e6b8-bf96-4048-95ea-37afe6263789aa221dbe-35d3-41af-ac21-701e9f3d33bfaed7002b-bcd9-471b-90c7-6528df8c2694c73b7849-8b27-45a6-8f8c-7b740a34a350c7828660-d451-4191-8da0-c3910c927211c7dc985e-7191-4222-89d3-65bc0ca59d52d07bf974-ae91-4993-85ed-96234c75bb78d60e65c0-207e-4348-b88b-aaf5faf4f667e33dd8ff-7437-4b5c-a7ae-842438ebec0eec0f3388-7700-4e5c-88b9-51b1aa345a70fa1e5da6-662b-440b-ae37-ce0caddd710bCanonical linkage remains open; the cited source assertion is retained below.
Vendor specified only by source · Product specified only by source
- Source class
- Nvd cpe vulnerable target
- Assertions
- 24
- Mapping revision
- cpe23-exact-mapping-v1
- Observed cutoff
- Oct 22, 2026
Retained assertion IDs
08b19487-fd2d-4788-a669-37f2dd57c7b8131d5a31-4d97-4a93-841a-c1c611bdf804165c3eae-fc6f-413b-bb7d-32cd7285fa8317cb7ffc-797b-453f-afb9-1a18b8d593542464f5ba-c821-48df-bf3c-e7439409ed1727df7c04-09ef-4454-994f-abd38442976329cc8f35-ca27-45f5-8d87-0028a5e3da642eb32914-2e37-4244-a1f3-5c6598ca477c3bcc1163-98c8-448c-97f2-8572bed204c744234f08-e7d6-43c9-8953-b5a27f9560b746d8e0f5-cfa0-49ba-ab0f-83c4c586dd395bc7f99d-690a-4856-b3d6-f93d7faf333c63bf648e-fe50-4018-b45f-a0c261371a156d51eaf4-65d0-403e-88b0-aff7ab2660966d9b12e6-cdc3-4f16-bb78-2663e12d625d8827f525-d9d3-4f70-8baf-d9a48aa5393298113f4c-ff92-4092-9199-732113a28f3d9abf9518-d1f3-45d0-ae0a-a8ae53d5cd7ab13961ee-e558-405b-b283-e22a99727962d686cf52-c10c-425f-b3a2-64abffb7e5b2e5d3f4eb-57a1-4baa-b2c4-69ae18e18822f8de3cca-ed01-4d7f-9b7b-68f725bcf1d6f974d503-8988-4a77-8db6-6f0770f14d45fb1f16dd-752f-4962-86c4-a5b9cf2ee4a1Assessments
CVSS by origin
AV:N/AC:M/Au:N/C:P/I:P/A:PCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:CDirect CVE/CNA normalized decisions
microsoft
CVSS 3.1 · Primary · Original assertion · rank 1
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C- Validation
- Valid match
- Recomputed
- 7.8
- Decision reason
- Evidence supported
- Policy
- casca-direct-cvss-eligibility-v1
Assessments are retained side by side under closed precedence. Cascade never averages CVSS.
Evidence boundaries
- KEV membership is authoritative for the catalog, not proof of exposure in any environment.
- EPSS is a dated model probability and not an individual-environment prediction.
- Affected or fixed status applies only to the exact cited product and version scope; remaining scope stays source-scoped.
- NVD-carried upstream facts remain derivative; independent corroboration requires a separately authored source.
- Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
- NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
- Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.
- OSV aggregation and OSV-converted NVD material are not independent corroboration.
- Red Hat facts are vendor assertions for the exact supplied products.
- Nonmembership and not-yet-observed states are not proof of safety.